1. Field of the Invention
The present invention is generally related to the area of image sensors and scanning technologies, and more particularly is related to image sensors with multiple bands suitable for use in various scanning applications including remote sensing.
2. Description of the Related Art
Remote sensing is related to the acquisition of information about an object or phenomenon without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth (both on the surface, and in the atmosphere and oceans).
There are two main types of remote sensing: passive remote sensing and active remote sensing. Passive remote sensing detects natural radiation that is emitted or reflected by the object or surrounding areas. Reflected sunlight is the most common source of radiation measured by passive sensors. Examples of passive remote sensors used in the passive remote sensing include film photography, infrared, and charge-coupled devices (CCD), and radiometers. Active remote sensing, on the other hand, emits energy in order to scan objects and areas whereupon a sensor then detects and measures the radiation that is reflected or backscattered from the target. RADAR is an example of active remote sensing, where the time delay between emission and return is measured, establishing the location, height, speed and direction of an object being radiated by the emitted energy (electromagnetic waves).
One of the passive remote sensing techniques is to use what is commonly referred to as remote sensing instrument (RSI) that includes multiple linear image sensors to capture a ground scene. A satellite map or image is then formed from respective signals from the multiple linear image sensors. For example, an exemplary RSI may use one panchromatic (PAN) signal and four Multi-Spectral (MS) signals from the multiple linear image sensors. In general, besides the PAN signal, there are four MS signals Blue (B), Green (G), Red (R), and Near Infrared (NIR), which are used to create a colorful satellite image.
In a high resolution and high performance RSI, the instrument needs 5 individual linear sensor arrays. The pixel size and number of pixel element are determined by the optical system for the individual linear sensor arrays, the satellite orbit and the swath width. For imagery at 720 km above the earth, the optical reduction is about 200,000. The pixel size of 10 um represents 2 meters resolution on the ground. For a linear sensor of 12,000 pixels, the image swath width is 24 km. The resolution of the PAN signal is normally higher than that of the MS signals. Thus the pixel size for the pixels generating the MS signals is typically larger and the pixel number is smaller than that of the pixel size for the pixels generating the PAN signal.
In the remote sensing applications, the current RSI uses folding mirrors to guide the different ray traces (incoming lights) to different optical planes, where one or more individual sensor arrays are positioned. FIG. 1 shows a mirror block to fold different ray traces (via respective filters) and project a corresponding colored ray onto one designated sensor array. Each of the MS CCD-based arrays is located on an independent optical plane. FIG. 2 shows another way to use folding mirrors to design a RSI. The folding mirror guiding the PAN ray trace to a PAN focal plane while the MS folding mirrors direct the MS ray traces to the MS focal planes. The focal planes of PAN and MS are different optical planes. The folding optical methods require very complicated optical system design.
As the sensor arrays used in the current RSI are commonly CCD-based devices while other circuits (e.g., AGC and amplifiers) are CMOS-based. It is well known that the integration of the CCD sensors and the CMOS-based circuitry requires very sophisticate skill sets given the working conditions in which a RSI operates. The RSI needs to operate in space, thus the RSI system designs are required to consider the thermal, structure and mechanical extremes in the space. These considerations and resulting design parameters often cause the RSI designs very complicated, hard to make and bulky.
There is thus a great need for different architectures of RSI that may have small footprint, broad operating wavelength range, enhanced impact performance, lower cost, and easier manufacturing process.
Likewise, such architectures may make it possible to be used in other applications such as detecting counterfeit currency or authenticating certain certificates or cards.